A woman?s fertility is dependent on the cascade of events leading up to ovulation. Defects in this ovulatory process result in 25% of all female infertility cases, supporting the paramount role of ovulation in reproductive success and providing a strong premise to explore mediators of the ovulatory process. We propose that neurotensin is one of these pivotal regulators of the ovulatory process. Ovulation is set in motion by the preovulatory LH surge which increases ovarian intrafollicular mediators that act to bring about oocyte release. Our novel and exciting preliminary data indicate that neurotensin (NTS), a small neuropeptide, is a key intrafollicular mediator of ovulation. This is based upon our findings that NTS is one of the most differentially-expressed genes in the granulosa cells of the human ovulatory follicle, up to 15,000 fold after the ovulatory gonadotropin surge. Likewise, LH also rapidly and significantly increases NTS mRNA in granulosa cells from rodent and monkey ovulatory follicles. Importantly, injection of a neurotensin antibody into monkey preovulatory follicles blocked oocyte release resulting in luteinized unruptured follicles, consistent with failure of ovulation. Similarly, mice lacking NTS expression form luteinized unruptured follicles following LH/hCG administration, and a NTS receptor antagonist inhibits oocyte release in a novel in vitro model of mouse ovulation. Yet, other than our preliminary data, nothing is known regarding the temporal expression of NTS receptors or the function of NTS in ovulation and female fertility. These questions will be addressed in this proposal through a collaborative approach utilizing the exceptional backgrounds, technical expertise, and models of the Project Leaders. We will make use of a high-impact, translational model where the granulosa and theca from human periovulatory follicles will be collected prior to and at three designated times after hCG (early, late and postovulatory) to complement in vivo and in vitro studies performed with mice and monkeys. The regulation of NTS and NTS receptor expression in the ovulatory follicle will be illuminated and compared across women, monkeys and mice in Aim 1. The ovulatory functions stimulated by NTS in granulosa, theca, cumulus, and endothelial cells of the follicle will be elucidated in Aim 2. The actions of NTS on ovulation, as well as other key reproductive processes, will be revealed in mice and monkeys using mice lacking NTS expression, NTS receptor antagonists, and NTS-neutralizing antibodies in Aim 3. A major strength of this proposal is the collaborative interactions between Dr. Curry and Dr. Duffy to address the function of NTS and its receptors in periovulatory events across multiple species, including exceptional human ovarian tissues and in vivo studies of non-human primates, an animal model with high relevance to human reproductive function. Thus, there is an exceptional degree of significance in understanding the basic tenets of oocyte release which provides a fundamental platform to either improve outcomes for infertile women or conversely provide targets to prevent oocyte release for female contraception.